Pipetting devices are in particular used in the laboratory for metering liquids. They are drawn into pipette tips through a tip orifice and dispensed. With air cushion pipettes a displacement device for a gas is incorporated in the pipetting device and communicatingly connected to the pipette tip by the attachment. An air cushion is displaced by means of the displacement device, so that liquid is suctioned into the pipette tip and ejected therefrom. The displacement device is generally a cylinder with a piston which can be displaced therein.
The pipette tips are releasably connected to the attachment, so that they can be exchanged after use for a fresh pipette tip. As a result contamination can be avoided during subsequent metering. Single use pipette tips are available cheaply, made from plastics.
The attachment for fastening pipette tips is frequently a cylindrical or conical projection relative to a base body or a housing, and onto which a pipette tip with a suitable mounting opening or receiver can be clamped. This can take place without grasping the pipette tip by pressing the attachment into the mounting opening of the pipette tip which is ready in a holder.
To avoid contamination of the user, pipette devices comprise an ejection device with a drive device and a throw-off device. By actuating the drive device the throw-off device is displaced, such that it releases the pipette tip from the attachment, without it having to be grasped by the user. Frequently, the drive device has a mechanism which has to be manually actuated by means of an actuation button, in order to release the pipette tip from the attachment. Drive devices are also possible with an electromotive drive. Releasing the pipette tip from the attachment can require increased operating force, in particular with pipette tips which are rigidly clamped onto the attachment. Even with one-channel systems, ie pipetting devices which comprise a single attachment for a single pipette tip, this can make ejecting the pipette tip from the attachment difficult or impossible. Particularly high operating force can be required with multi-channel pipette systems which have a plurality of parallel attachments for mounting pipette tips, due to multiple tip ejection forces.
A pipette system with an axially movable throw-off device for releasing a pipette tip from an attachment, a drive device to drive the axial movements of the throw-off device and a pull-means gear, push-means gear or linkage gear transferring an axial drive movement of the drive device into an axial movement of the throw-off device is known from EP 0 992 288 A2. The force exerted by the throw-off device on the pipette tip exceeds the force exerted by the user, whereby the ejection is facilitated.
Air cushion pipettes can lead to contamination of the displacement device. Penetration of fluid due to improper handling or the rising of vapour or tiny droplets of the liquid to be pipetted into the displacement device can result therefrom. Moreover, it can be desirable to exchange the displacement device in order to prepare the pipetting device for use in a further area of the volume of liquids to be pipetted.
Pipetting devices are already known in which the displacement device with the attachment for mounting the pipette tip can be separated from a drive device to drive the displacement device. In EP 0 428 500 B1 such a pipetting device is disclosed in which the displacement device can be screwed onto a shank of the drive device by means of a coupling nut. In principle, it is therefore possible to release the displacement device for cleaning or for exchanging the drive device. The fastening is nevertheless laborious, time-consuming and susceptible to faults.
Proceeding from this, the object of the invention is to provide a pipetting device in which the displacement device and the drive device can be more easily and more rapidly connected to and separated from one another and in which the connection is less susceptible to faults.
The object is achieved by a pipetting device with the features of claim 1. Advantageous embodiments of the pipetting device are revealed in the sub-claims.